linux-kernel - Re: [RFC] Recursive printk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 6 Dec 2008 08:33:05 +0100
From:	Willy Tarreau <w@....eu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nick Andrew <nick@...k-andrew.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Takashi Iwai <tiwai@...e.de>
Subject: Re: [RFC] Recursive printk

On Fri, Dec 05, 2008 at 11:20:16PM -0800, Andrew Morton wrote:
> > void snd_verbose_printk(const char *file, int line, const char *format, ...)
> > {
> >         va_list args;
> > 
> >         if (format[0] == '<' && format[1] >= '0' && format[1] <= '7' && format[2] == '>') {
> >                 char tmp[] = "<0>";
> >                 tmp[1] = format[1];
> >                 printk("%sALSA %s:%d: ", tmp, file, line);
> >                 format += 3;
> 
> That's racy.  Two threads can fight over tmp[1].  It should do:
> 
> 		printk("<%c>ALSA %s:%d: ", format[1], tmp, file, line);
> 
> (I didn't know that you can even modify literal strings - shouldn't
> they be in read-only storage?)

no Andrew, this tmp[] is declared on the stack, and gcc emits code to
copy the constant "<0>" onto the stack every time this code is called
(which is basically just a 32-bit integer copy). So there's no race
either.

Regards,
Willy

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/